The process of epidermal differentiation produces a smooth layer of dead cells at the surface, and these stratum corneum cells are continually shed distally and replenished proximally. Little is known about the control of such shedding in either normal persons or in those with diseases causing derangement of shedding, and little is known about the forces causing the cells to adhere to each other. The recent discovery of steroid sulfatase deficiency in patients with recessive X-linked ichthyosis offers an approach to examining the biochemistry of normal and abnormal shedding. The proposed research will examine details of sulfated sterol and steroid metabolism in the skin and plasma of patients with recessive S-lined ichthyosis, the distribution and control of the enzyme activity and of enzyme protein, the effects of sulfated sterols on cellular aggregation and adhesion, and possible interrelationships between stratum corneum shedding, ultraviolet irradiation, and vitamin D metabolism.